Converting a Map [String, Any] to a Case Class Using Shapeless

Question

The question here asks about mapping the case class to Map [String, Any]. I was wondering what would be the other way around, transforming Map [String, Any] into a case class. Given the following card:

val mp = Map("name" -> "Tom", "address" -> Map("street" -> "Jefferson st", "zip" -> 10000)) 

Convert it to the case Person class:

 case class Person(name:String, address:Address) case class Address(street:String, zip:Int) val p = Person("Tom", Address("Jefferson st", 10000)) 

with something like this:

 val newP = mp.asCC[Person] assert(newP.get == p) 

How do I do this with Shapeless.

Answer 1

Here, a mostly unverified solution is deferred. First for a class like:

 import shapeless._, labelled.{ FieldType, field } trait FromMap[L <: HList] { def apply(m: Map[String, Any]): Option[L] } 

And then the instances:

 trait LowPriorityFromMap { implicit def hconsFromMap1[K <: Symbol, V, T <: HList](implicit witness: Witness.Aux[K], typeable: Typeable[V], fromMapT: Lazy[FromMap[T]] ): FromMap[FieldType[K, V] :: T] = new FromMap[FieldType[K, V] :: T] { def apply(m: Map[String, Any]): Option[FieldType[K, V] :: T] = for { v <- m.get(witness.value.name) h <- typeable.cast(v) t <- fromMapT.value(m) } yield field[K](h) :: t } } object FromMap extends LowPriorityFromMap { implicit val hnilFromMap: FromMap[HNil] = new FromMap[HNil] { def apply(m: Map[String, Any]): Option[HNil] = Some(HNil) } implicit def hconsFromMap0[K <: Symbol, V, R <: HList, T <: HList](implicit witness: Witness.Aux[K], gen: LabelledGeneric.Aux[V, R], fromMapH: FromMap[R], fromMapT: FromMap[T] ): FromMap[FieldType[K, V] :: T] = new FromMap[FieldType[K, V] :: T] { def apply(m: Map[String, Any]): Option[FieldType[K, V] :: T] = for { v <- m.get(witness.value.name) r <- Typeable[Map[String, Any]].cast(v) h <- fromMapH(r) t <- fromMapT(m) } yield field[K](gen.from(h)) :: t } } 

And then a helper class for convenience:

 class ConvertHelper[A] { def from[R <: HList](m: Map[String, Any])(implicit gen: LabelledGeneric.Aux[A, R], fromMap: FromMap[R] ): Option[A] = fromMap(m).map(gen.from(_)) } def to[A]: ConvertHelper[A] = new ConvertHelper[A] 

And an example:

 case class Address(street: String, zip: Int) case class Person(name: String, address: Address) val mp = Map( "name" -> "Tom", "address" -> Map("street" -> "Jefferson st", "zip" -> 10000) ) 

And finally:

 scala> to[Person].from(mp) res0: Option[Person] = Some(Person(Tom,Address(Jefferson st,10000))) 

This will only work for case classes whose members are Typeable or other case classes whose members are either Typeable or other case classes ... (etc.).